Method for producing grain-oriented electrical steel sheet, and induction heating device

Abstract

A method for producing a grain-oriented electrical steel sheet is disclosed including hot rolling a steel material to obtain a hot-rolled sheet, subjecting the hot-rolled sheet to one cold-rolling step, or two or more cold-rolling steps with intermediate annealing interposed between each cold-rolling step so as to obtain a cold-rolled sheet with a final thickness, and subjecting the cold-rolled sheet to decarburization annealing which also serves as primary recrystallization annealing and then to finishing annealing, in which the decarburization annealing includes a heating step in which the steel sheet is rapidly heated at an average heating rate of 250° C./s or more from 400° C. to a temperature T(° C.) of 700 to 900° C. and then held at a heating rate of ⅔ of the average heating rate or less in any of temperature ranges between 500° C. and 700° C. for a time of 0.10 seconds or more but less than 1.00 seconds.

1 . A method for producing a grain-oriented electrical steel sheet, comprising:
 hot rolling a steel material to obtain a hot-rolled sheet;   subjecting the hot-rolled sheet to one cold-rolling step, or two or more cold-rolling steps with intermediate annealing interposed between each cold-rolling step so as to obtain a cold-rolled sheet with a final thickness; and   subjecting the cold-rolled sheet to decarburization annealing which also serves as primary recrystallization annealing and then to finishing annealing,   characterized in that   the decarburization annealing includes a heating step in which the steel sheet is rapidly heated at an average heating rate of 250° C./s or more from 400° C. to a temperature T(° C.) of 700 to 900° C. and then held at a heating rate of ⅔ of the average heating rate or less in any of temperature ranges between 500° C. and 700° C. for a time of 0.10 seconds or more but less than 1.00 seconds.   
     
     
         2 . The method for producing a grain-oriented electrical steel sheet according to  claim 1 , wherein
 the steel material has a component composition containing elements of a following group A or B, with a balance being Fe and unavoidable impurities:
 group A: C: 0.01 to 0.10 mass %, Si: 2.0 to 4.5 mass %, Mn: 0.01 to 0.50 mass %, Al: 0.0100 to 0.0400 mass %, N: 0.0050 to 0.0120 mass %, and at least one of S and Se: a total of 0.01 to 0.05 mass %, and 
 group B: C: 0.01 to 0.10 mass %, Si: 2.0 to 4.5 mass %, Mn: 0.01 to 0.50 mass %, Al: less than 0.0100 mass %, N: 0.0050 mass % or less, S: 0.0070 mass % or less, and Se: 0.0070 mass % or less. 
   
     
     
         3 . The method for producing a grain-oriented electrical steel sheet according to  claim 2 , wherein
 the steel material further contains, in addition to the component composition, at least one element selected from the group consisting of Sb: 0.500 mass % or less, Cu: 1.50 mass % or less, P: 0.500 mass % or less, Cr: 1.50 mass % or less, Ni: 1.500 mass % or less, Sn: 0.50 mass % or less, Nb: 0.0100 mass % or less, Mo: 0.50 mass % or less, B: 0.0070 mass % or less, and Bi: 0.0500 mass % or less.   
     
     
         4 . The method for producing a grain-oriented electrical steel sheet according to  claim 1 , wherein
 the rapid heating in the decarburization annealing is performed using a transverse induction heating device.   
     
     
         5 . A transverse induction heating device for use in the method for producing a grain-oriented electrical steel sheet according to  claim 4 , comprising
 a heating coil having a shape of a rounded rectangle including two parallel lines of equal length lying along a sheet width direction, and two semicircles, wherein   relationships of R 1 ≥w and R 2 <v are satisfied, where R 1  represents a maximum inner diameter (m) of the heating coil in the sheet width direction, R 2  represents a maximum inner diameter (m) of the heating coil in a threading direction, w represents a width (m) of the steel sheet, and v represents a threading speed (m/s) of the steel sheet.   
     
     
         6 . The method for producing a grain-oriented electrical steel sheet according to  claim 2 , wherein
 the rapid heating in the decarburization annealing is performed using a transverse induction heating device.   
     
     
         7 . The method for producing a grain-oriented electrical steel sheet according to  claim 3 , wherein
 the rapid heating in the decarburization annealing is performed using a transverse induction heating device.   
     
     
         8 . A transverse induction heating device for use in the method for producing a grain-oriented electrical steel sheet according to  claim 6 , comprising a heating coil having a shape of a rounded rectangle including two parallel lines of equal length lying along a sheet width direction, and two semicircles, wherein
 relationships of R 1 ≥w and R 2 <v are satisfied, where R 1  represents a maximum inner diameter (m) of the heating coil in the sheet width direction, R 2  represents a maximum inner diameter (m) of the heating coil in a threading direction, w represents a width (m) of the steel sheet, and v represents a threading speed (m/s) of the steel sheet.   
     
     
         9 . A transverse induction heating device for use in the method for producing a grain-oriented electrical steel sheet according to  claim 7 , comprising a heating coil having a shape of a rounded rectangle including two parallel lines of equal length lying along a sheet width direction, and two semicircles, wherein
 relationships of R 1 ≥w and R 2 <v are satisfied, where R 1  represents a maximum inner diameter (m) of the heating coil in the sheet width direction, R 2  represents a maximum inner diameter (m) of the heating coil in a threading direction, w represents a width (m) of the steel sheet, and v represents a threading speed (m/s) of the steel sheet.